Cache Update Algorithm

By default, without the cache_version attribute, applet caching will be updated if:

• The cache_archive has not been cached before, or

• The "Last-Modified" value of the cache_archive on the web server is newer than the one stored locally in the applet cache, or

• The "Content-Length" of the cache_archive on the web server is different than the one stored locally in the applet cache.

However, in some situations, the "Last-Modified" value returned from the web server through HTTP/HTTPS may not reflect the actual version of the applets. For example, if the web server crashes and all the files are restored, the cache_archive will have a different modification date on the server. Even if the cache_archive has not been updated, it will still force all the Java Plug-in clients to download the cache_archive again.

To strongly enforce the version update, it is recommended that the applet deployer use the cache_version attribute.

If cache_version is used, applet caching will be updated if the cache_version for the cache_archive in the EMBED/OBJECT tag is larger than the one stored locally in the applet cache. Note that the version number is used for triggering an update; there is no actual version number attached to the .jar file on the web server. In fact, unless version is used to trigger an update, it is possible the applet on the web server could be updated without the applet in cache_archive.

Using cache_version eliminates the need to connect to the web server to obtain "Last-Modified" and "Content-Length" of the cache_archive. In most cases this will speed up performance.